Marylaxd Gkological Survey 387 



B. cumberlandice may be mistaken for immature R. marylandica, but a 

 comparison of equally young specimens shows that the latter are always 

 marked by faint radial striations. Elongate specimens of B. suessana 

 may also be identified as R. cumherlandice, but here again the almost com.- 

 plete absence of the radial striis in the latter distinguishes them. 



Length 2.3 cm. ; width 1.8 cm. 



Occurrence. — Oriskany Formation, Eidgely Member. Cumberland. 



CollecUons. — Maryland Geological Survey, American Museum of 

 Natural Ilistoiy, U. S. National Museum. 



Eexsseljeria (Beachia) suessana (Hall) 

 Plate LXVII, Figs. 7-15 



Meganteris suessana Hall, 1857, Tenth Ann. Kept. N. Y. State Cab. Nat. Hist., 



p. 100. 

 Rensselwria suessana Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 459, pi. cvii, 



figs. 1-15, 1861. 

 R. (Beachia) suessana Hall and Clarke, 1893, ibidem, vol. viii, pt. li, p. 260. 



pi. Ixxvii, figs. 1-11. 

 Beachia suessana Weller, 1903, Geol. Surv. N. J., Pal., vol. iii, p. 352, pi. xlvii, 



figs. 5-14. 



Description. — " Shell longitudinally obovate, varying to oval or sub- 

 elliptical, somewhat compressed; valves nearly or quite equal; no traces 

 of a sinus on either valve ; front narrowly rounded ; lateral margins very 

 abruptly inflected : ventral valve depressed convex, most prominent along 

 the middle, sloping very gradually towards the sides; beak pointed, small, 

 very angular along its lateral borders, incurved, rising above the hinge-line 

 but not touching the other valve, perforate in the apex by a small round 

 aperture partly completed by the two small deltidial pieces, which, to- 

 gether with the thickened dental apophyses of the opposite valve, close 

 the triangular foramen below: dorsal valve symmetrically depressed 

 convex, sloping very gradually from near the middle laterally and towards 

 the front, rounding a little more abruptly towards Ihe beak, which is 

 pointed and scarcely incurved : hinge-line nearly straight, or sloping from 

 the beaJc at a very obtuse angle, much less than the width of the shell. 

 Surface usually appearing to be smooth, but, on well-preserved specimens, 

 remains of very faint simple radiating strias may be seen towards the 

 margin, which always become obsolete above." Hall, 1857. 



